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Dinosaurs of the Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish gray, or red. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period. Table key Ornithischians The herbivorous ornithischian dinosaurs were diverse but not as common as sauropods in the Morrison. Unclassified members include the "Fruita Echinodon", a possible heterodontosaurid, and the dubious Tichosteus lucasanus and T. aequifacies. Plate-backed stegosaurids included Hesperosaurus mjosi, Hypsirophus discursus, Stegosaurus armatus (?including S. ungulatus), S. stenops, and "S." longispinus. Armored dinosaurs that weren't stegosaurs were unknown in the formation until the 1990s. Two have been named: Gargoyleosaurus parkpinorum and Mymoorapelta maysi. Ornithopods, bipedal herbivores, came in several types. Small "hypsilophodonts" included Drinker nisti, Laosaurus celer, "L." gracilis, Nanosaurus agilis, Othnielia rex, and Othnielosaurus consors. Larger but similar-looking dryosaurids were represented by Dryosaurus altus and the camptosaurid Camptosaurus aphanoecetes, which is currently known only from Dinosaur National Monument. Still larger was the more common Camptosaurus dispar, probably including Brachyrophus altarkansanus and Symphyrophus musculosus. Dryosaurids and camptosaurids were early iguanodonts, a group that would later spawn the duck-billed dinosaurs. Indeterminate ornithischian remains present in Utah, USA. Ornithopods Thyreophorans Misc Sauropods Sauropods, the giant long-necked long-tailed four-legged herbivorous dinosaurs, are among the most common and famous Morrison fossils. A few have uncertain relationships, like [[Apatosaurus|"Apatosaurus" minimus]] (possibly an early titanosaur) and Haplocanthosaurus. Sauropods including Haplocanthosaurus priscus, H. delfsi, and the diplodocids Dystrophaeus and Eobrontosaurus appeared in the early stages of the Morrison. The middle stages were dominated by familiar forms such as the Giraffe-like Brachiosaurus altithorax, which were uncommon, but related camarasaurids, like Camarasaurus supremus, C. grandis, C. lentus, and C. lewisi, were very common. Also common were long, low diplodocids, like Apatosaurus ajax, A. excelsus (formerly "Brontosaurus"), A. louisae, A. parvus, Atlantosaurus montanus, Barosaurus lentus, Diplodocus longus, D. carnegii, "D." hayi, "D." lacustris, Dyslocosaurus polyonychius. By the late Morrison, gigantic diplodocids (or likely diplodocids) had appeared, including Diplodocus hallorum (formerly Seismosaurus), Supersaurus vivianae, Amphicoelias altus, and the largest of all, A. fragilimus. Smaller sauropods, such as Suuwassea emiliae from Montana, tend to be found in the northern reaches of the Morrison, near the shores of the ancient Sundance Sea, suggesting ecological niches favoring smaller body size there compared with the giants found further south.Harris, J.D. and Dodson, P. (2004). "A new diplodocoid sauropod dinosaur from the Upper Jurassic Morrison Formation of Montana, USA." Acta Palaeontologica Polonica, 49(2): 197–210. Possible indeterminate diplodocid remains present in Utah. Indeterminate sauropod remains are present in Utah. Diplodicoids Apatosaurines Macronarians Theropods Theropod dinosaurs, the carnivorous dinosaurs, came in several different types. The less derived types, the ceratosaurs and megalosaurids, included Ceratosaurus nasicornis, C. dentisulcatus, C. magnicornis, Elaphrosaurus sp., and the megalosaur Torvosaurus tanneri (?including Edmarka rex). Allosaurids included the common Allosaurus fragilis (including Epanterias amplexus), A. new species, Antrodemus valens, and giant Saurophaganax maximus. Indeterminate theropod remains have been recovered in Utah. Indeterminate theropod tracks have been recovered from both Utah and Arizona. Carnosaurs Ceratosaurs Coelurosaurs Coelurosaurs, more derived types more closely related to birds, included Coelurus fragilis, Ornitholestes hermanni, Tanycolagreus topwilsoni, the possible troodontid Koparion douglassi, and the definite troodontid WDC DML 001. There was also the possible early tyrannosaur relative Stokesosaurus clevelandi. Marshosaurus bicentesimus was a medium-sized theropod of uncertain classification that may have been related to the allosaurids. Misc Eggs Dinosaur eggs have been found in Utah. Tracks Ornithopods Morrison ornithopod trace fossils are represented by three toed tracks which are generally small. The toes of Morrison ornithopod tracks are usually more widely splayed than the theropod tracks preserved in the formation. Stegosaurs Stegosaur tracks were first recognized in 1996 from a hindprint-only trackway discovered at the Clevland-Lloyd quarry, which is located near Price, Utah."Walk and Don't Look Back: The Footprints; Stegosaurs" Foster (2007) pg. 238 Two years later, a new ichnogenus called Stegopodus was erected for another set of stegosaur tracks which were found near Arches National Park, also in Utah. Unlike the first, this trackway preserved traces of the forefeet. Fossil remains indicate that stegosaurs have five digits on the forefeet and three weight-bearing digits on the hind feet. From this, scientists were able to successfully predict the appearance of stegosaur tracks in 1990, six years in advance of the first actual discovery of Morrison stegosaur tracks. Since the erection of Stegopodus, more trackways have been found, however none have preserved traces of the front feet, and stegosaur traces remain rare. Theropods Indeterminate theropod tracks have been recovered from both Utah and Arizona. Footnotes References * Carpenter, K. and Wilson, Y. (2008). A new species of Camptosaurus (Ornithopoda: Dinosauria) from the Morrison Formation (Upper Jurassic) of Dinosaur National Monument, Utah, and a biomechanical analysis of its forelimb. Annals of the Carnegie Museum 76:227-263 PDF * Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. 389pp. ISBN 978-0-253-34870-8. * Galton , P.M. (1981). Dryosaurus, a hypsilophodontid dinosaur from the Upper Jurassic of North America and Africa. Postcranial skeleton. Palaeontol. Z. 55(3/4), 271-312 * Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 543–545. ISBN 0-520-24209-2. Category:Dinosaurs Category:Taxonomy Category:Geologic formations Category:Fossil Formations